Mechanical stresses imposed on weightbearing synovial joints are implicated in the development of joint disease and in failures of prosthetic joint replacements. Studies of these stress distributions are necessary to understand the degenerative process, to evaluate therapeutic procedures, and to optimize implant design. The proposed investigation will provide three-dimensional finite element stress analyses of the human knee joint. Three cases will be considered: a) the normal knee; b) the degenerative knee; and c) the prosthetic total knee replacement. Both condylar and hinged type prostheses will be compared. Joint geometries and material properties for use in the analyses will be determined from excised human knees obtained from autopsy and amputation specimens. Theoretically predicted stress distributions in the proximal tibia will also be verified with experimental data from instrumented compression tests and low cycle fatigue tests on excised knees. The verified analyses will then be used to conduct studies on the pathomechanics of osteoarthritis by systematically varying joint material properties in the finite element models. Predicted stress distributions will be compared to microscopic observations of degenerative change in the excised knees and in joint surfaces removed during reconstructive surgery. The finite element analyses will then be used to evaluate the effects of tibial osteotomies and the use of canes and crutches on stresses in the proximal tibia. The analyses will also be used to suggest optimized implantation techniques and fixation methods for prosthetic knee joint replacements.